Does yours squat to the bump stops when you put 300lbs in the bed. Mine does. What about your boat. Squats like it's overloaded with fat chicks.

Nope. LTZ has Autoride with load leveling. Sits perfectly level with the boat. Haven't had 3000lbs in the bed but have had around 2k and it still sat level. Rides great both loaded and unloaded. What year is yours?

New(er) F150's have really light rear springs as well. I've run overloads on my last 3 company trucks because they wouldn't hold up an 80gal transfer tank and a tool box, combined weight less than 1000lbs and all ahead of the rear axle.
My new 2011 company F150 is even softer I swear. Had maybe 500lbs of traffic control gear in the back and it looked like I lowered it. The new 5.0 and 6sp auto is bad ars though. Ferd finally got it right with that setup I think!
Don't let that stop you with any leaf sprung truck though (not sure if the Avy is leafs or coils). A cheap set of helper springs will make all the difference in the world. Coils are easy to beef up with a set of airbags for a couple hundo as well.
If you're looking used, why not just look private party? You're never going to get a better deal thru a dealer. Factory warranty is factory warranty regardless of who you buy it from if you're looking new enuff to have a warranty. No salesman bs, find the one you like, phone the guy up and go check it out. Alot easier to cut down on how much sales tax you have to pay if you buy private party too (if you catch my drift) unless you're financing a big chunk of it of course.
Plus you're in TX, there should be good used private party trucks coming our your @ss down there, right? Especially with gas prices up again.

I spent 2 weeks working at a dealership in Dallas. Oh my, what a bunch of sleaze bags. I was 20 years old and one day after a rant from the sales manager, I just handed him my badge and left. Find what you want and let them work for you. Good luck. I love my 2009 Suburban LTZ

Recently, a friend of mine was shopping for a new ride, knew what he wanted, what options would work for him and he had the cash. He sent the online sales guys at every dealer in our area that carried that brand and told them what he was looking for and asked for their best offer. He would then send the best offer he received back out to the list. He repeated this until the price was only going down $50 at a time and sent one last email saying that the first response he got at that price would get his business.

Regarding new vehicles being a bad financial decision, many consumer experts have made the case that some new vehicles are a better deal than some 1-3 yr old used vehicles, due to the shortage of used vehicles for sale and the soft new vehicle market.